1. Technical Field
The present invention relates to a plasma processing system for generating an active gas containing ions, free radicals, atoms and molecules by plasma discharge and performing a plasma process onto a solid, powder and gas by the active gas.
2. Discussion of Related Art
Plasma discharge is used for gas excitation to generate an active gas containing ions, free radicals, atoms and molecules. The active gas is generally used in various fields, and typically, in semiconductor fabrication processes such as etching, deposition and cleaning.
Plasma sources for generating plasmas are various, and typical examples thereof are the capacitively coupled plasma source and the inductively coupled plasma source, both using the radio frequency. The inductively coupled plasma source relatively easily increases the ion density as the radio frequency power increases. Due to this reason, the inductively coupled plasma is suitable for generating high-density plasma.
However, since energy coupled with plasma is lower than supplied energy, a method for the inductively coupled plasma uses a driving coil with very high voltage. As a result, ion energy is high, and thus an inside surface of a plasma reactor is likely to be damaged by ion bombardment. The damage to the inside surface of the plasma reactor by the ion bombardment causes a negative result of acting as a pollution source in plasma processing. When lowering the ion energy, the energy coupled with plasma is getting much lower, thereby frequently occurring plasma to be off. This makes it difficult to stably maintain plasma.
Stable maintenance of plasma is a very important matter connected directly with productivity. When plasma is off during a process due to any reasons, the process fails. Then, it needs to again initialize the process to re-start the process. Specifically, when power supplied to a radio frequency generator is off due to unstable power supply such as a momentary power failure, the plasma of a plasma reactor is off, and the process is discontinued. Wafer substrates for fabrication of semiconductor devices or glass substrates for liquid crystal displays have become larger. In this situation, a loss rate resulting from a single process failure gets higher.
In a semiconductor fabrication process, specifically, in a process using plasma, remote plasma is very useful. For example, remote plasma is very valuably used in a cleaning process of a process chamber or an ashing process for a photoresist strip. As a substrate to be processed becomes larger, the volume of a process chamber increases. In this regard, a plasma source should be capable of sufficiently supplying a high-density active gas in a remote manner, and maintaining plasma very stably.
To generate and provide high-density plasma in large quantities, the volume of a plasma reactor also increases. A remote plasma reactor is generally installed above a process chamber. However, when the size of the reactor becomes bigger, it is not easy to install the reactor. Furthermore, it is more difficult to install a conventional plasma reactor which is formed as one unit with a radio frequency generator.